1. Field
This invention is generally related to wireless communications, and more particularly, to techniques for reducing or eliminating DC (direct current) offset in transmission paths.
2. Background
Signal paths in radio frequency (RF) transmitters sometimes have undesirable DC offsets. DC offset often refers to a relatively constant offsetting of a signal from zero. In other circumstances, DC offset may alternatively refer to offsetting that occurs between differential signals. In contemporary digital communication systems, such as mobile cellular systems, the latter type of DC offset, that occurring between differential signals, may be particularly problematic. For example, in digital communication systems transmitting in-phase (I) and quadrature (Q) signal components, undesirable DC offsets may occur between differential signals representing the I and Q components, such as Ip, Im, Qp and Qm differential signals. Such DC offsets may result in LO (local oscillator) carrier leakage and a degradation of EVM (error vector magnitude).
A DC offset may be due to mismatches in a signal path. For example, the DC offset may be due to mismatches between circuit components and/or leakage from circuit components along the path. DC offsets are typically inherent, undesirable aspects of active analog circuitry that generally must be eliminated or reduced before the signal is up-converted and transmitted.
Various techniques have been employed to minimize DC offset in transmitters. However, the previous attempts remain inadequate to address the DC offsets found in certain communication technologies, such as mobile cellular systems.